The present invention pertains to dealing with measurements taken at unevenly-spaced intervals in a computer network, and deriving a frequency spectrum from these measurements.
Many companies, such as Agilent Technologies, Hewlett-Packard, and others, support sensor nodes based on IEEE 1451 standards. Such standards allow the deployment of sensors on networks ranging from dedicated Ethernet local area networks to corporate internets to the World Wide Internet.
Current TCP/IP networks currently offer no quality-of-service guarantees. This causes a problem for many measurement applications, such as difficulty taking measurements at accurate and pre-determined time intervals.
U.S. Pat. No. 5,566,180 to Eidson et. al. teaches a method and apparatus for providing precise control of timing in distributed nodes in a network. U.S. Pat. No. 6,278,710 to Eidson provides further enhancement to time synchronization protocols for a distributed system.
These protocols provide the ability to accurately timestamp measurements taken by nodes on a network. Nevertheless, the times that measurements are taken may not be evenly spaced.
Many applications require the processing of data comprising sequences of such timestamped measurements. But many commonly used applications, such as signal processing algorithms, operate on data collected at evenly spaced times. One such common signal processing task is providing spectral data through the calculation of a Fourier Transform. What is needed is a method of calculating Fourier Transforms on unevenly spaced timestamped network data.
Spectrum estimates of unevenly spaced timestamped network data are calculated using estimates of a Continuous Fourier Transform. If the time between samples is long, the estimates may be computed incrementally.